1. Field of the Invention
The present invention relates to an internal combustion engine, a vehicle, a marine vessel, and a secondary air supply method for an internal combustion engine.
2. Description of the Related Art
Secondary air supply systems for supplying air to an exhaust path of an internal combustion engine are known. A secondary air supply system supplies air to exhaust gas of a high temperature to combust hazardous carbon monoxide or hydrocarbon in the exhaust gas and thus to provide harmless water or carbon dioxide. The secondary air supply system also supplies air to a portion of an exhaust path which is upstream with respect to a catalyst for cleaning the exhaust gas to promote the oxidation reaction in the catalyst. Japanese Laid-Open Patent Publication No. 09-324624 proposes a secondary air supply system for supplying, using a lead valve, air utilizing a negative pressure in an exhaust path. Japanese Laid-Open Patent Publication No. 07-205890 proposes a system for forcibly supplying air to an exhaust path using a pump, instead of the negative pressure in the exhaust path. The pump is driven using a portion of an output from the internal combustion engine.
In the system using the negative pressure described in Japanese Laid-Open Patent Publication No. 09-324624, unlike in the system described in Japanese Laid-Open Patent Publication No. 07-205890 including a pump for forcibly supplying air to the exhaust path, it is not necessary to drive a pump. Thus, the loss of the internal combustion engine output is small. However, when the internal combustion engine is driven in a high load state, the pressure in the exhaust path in the vicinity of the exhaust port becomes high and a sufficient amount of air cannot be supplied. By contrast, in the system described in Japanese Laid-Open Patent Publication No. 07-205890 including a pump for forcibly supplying air to the exhaust path, even when the internal combustion engine is driven in a high load state, air can be supplied. However; since the pump is driven by the internal combustion engine, the loss of the internal combustion engine output is large.